IGF-1 LR3 vs Retatrutide
A detailed comparison to help you understand the differences and choose the right peptide for your research goals.
IGF-1 LR3
IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a modified version of IGF-1 with extended half-life and enhanced potency. The modifications prevent binding to IGF binding proteins, increasing bioavailability.
Full details →Retatrutide
Retatrutide (LY3437943) is a first-in-class triple agonist peptide targeting GIP, GLP-1, and glucagon receptors simultaneously. Developed by Eli Lilly, it is currently in Phase 3 clinical trials and has demonstrated the highest weight loss of any obesity medication to date — up to 28.7% body weight reduction at 48 weeks. The triple-receptor mechanism represents the next evolution beyond dual agonists like tirzepatide.
Full details →Side-by-Side Comparison
| Aspect | IGF-1 LR3 | Retatrutide |
|---|---|---|
| Dose Range | 20 mcg–100 mcg | 4 mg–12 mg |
| Frequency | 1x daily | Less than daily |
| Cycle Length | 4–6 weeks | — |
| Route | subcutaneous | subcutaneous |
| Mechanism | Binds to IGF-1 receptors to promote protein synthesis, muscle growth, and fat metabolism. The LR3 modification (13 amino acid extension and arginine substitution) extends half-life from minutes to 20-30 hours. | Retatrutide is a synthetic peptide that activates three incretin/metabolic hormone receptors: (1) GLP-1 receptor — appetite suppression, insulin secretion, delayed gastric emptying, (2) GIP receptor — enhanced insulin sensitivity, improved fat metabolism, (3) Glucagon receptor — increased energy expenditure, hepatic fat mobilization, thermogenesis. The glucagon receptor component is the key differentiator, adding an energy-expenditure mechanism absent from GLP-1 and dual GIP/GLP-1 agonists. The molecule uses a C20 fatty diacid for albumin binding, enabling once-weekly dosing. |
| Typical Dosage | Research protocols typically use 20-100mcg daily, often divided into multiple injections or administered bilaterally to target muscles. | Phase 2 trial doses: 0.5 mg, 4 mg, 8 mg, and 12 mg weekly. The 12 mg dose produced maximum weight loss (28.7%). Phase 3 trials are evaluating doses up to 12 mg. Dose escalation schedule similar to other GLP-1s (start low, increase every 4 weeks). Final approved dosing not yet established — Phase 3 trials ongoing. |
| Administration | Intramuscular injection (site-specific growth) or subcutaneous for systemic effects. Often cycled 4-6 weeks on, equal time off. | Subcutaneous injection, once weekly. Phase 3 trials use pre-filled single-dose pens. Not yet commercially available — estimated FDA approval ~2027-2028. |
| Side Effects | Hypoglycemia, joint pain, water retention, potential jaw/hand growth with extended use, and injection site reactions. | Phase 2 data: nausea (up to 25%), diarrhea (up to 22%), vomiting (up to 15%), constipation, decreased appetite. GI side effects were dose-dependent and generally mild-to-moderate. Lower rates of nausea compared to semaglutide, potentially due to GIP component. Increased heart rate observed at higher doses. |
| Best For |
Key Differences
Unique to IGF-1 LR3:
Unique to Retatrutide:
Key Studies
IGF-1 LR3
- IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep.
American journal of physiology. Endocrinology and metabolism, 2025
- Revolutionary decellularized Alstroemeria stem-based nerve conduit integrated with GelMA and controlled IGF-1 LR3 release for enhanced rat sciatic nerve regeneration.
International journal of biological macromolecules, 2025
- Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets.
Journal of developmental origins of health and disease, 2023
Retatrutide
- Retatrutide in type 2 diabetes mellitus and obesity: an overview.
Expert review of clinical pharmacology, 2026
- Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trials.
Diabetes, obesity & metabolism, 2026
- Rationale, design and baseline characteristics of the TRANSCEND-CKD trial of retatrutide in patients with chronic kidney disease.
Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association, 2026
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